1. Field of the Invention
The present invention relates generally to electrical protection devices, and particularly to electrical protection devices with mis-wire safety features.
2. Technical Background
Ground fault circuit interrupters (GFCIs), and arc fault circuit interrupters (AFCIs) are examples of protective devices in electric circuits. These devices may be disposed in a receptacle that is subsequently installed in a wall box. The receptacle has line terminals for connection to the power line, and load terminals for connection to a load. The protective device has interrupting contacts for breaking the connection between the line terminals and load terminals when the protective device detects a fault condition. The connection is broken to interrupt the load current and thereby remove the fault condition. Fault conditions include those that result in risk electrocution of personnel, or fire.
The load terminals include receptacle contacts and feed-thru terminals. The receptacle contacts are configured to accommodate the blades of an attachment plug, which are inserted to provide power to a load. Feed-thru terminals, on the other hand, are configured to accommodate wires which are connected to one or more additional receptacles, known as a downstream receptacles. The downstream receptacle may include a string of downstream receptacles that comprise a branch circuit of an electrical distribution system.
In a typical related art approach, the receptacle contacts and feed-thru terminals remain electrically connected irrespective of whether the interrupting contacts are open or closed. Should the power line be improperly connected to the feed-thru terminals, e.g., mis-wired, the receptacle contacts remain energized even if one of the predetermined fault conditions is present in the load that is connected to the receptacle contacts via the plug connector. One drawback to this approach is that a mis-wire condition results in the receptacle contacts not being protected from a fault condition.
In another approach that has been considered, the lack of protection to the receptacle terminals when the protective device is mis-wired has only been partially addressed. This approach employs a circuit that prevents interrupting contacts from remaining closed when the protective device has been mis-wired. Since the interrupting contacts do not remain closed, there is lack of power to the down-stream receptacles which are connected to the line terminals. Typically, the open or closed condition of the interrupting contacts are visually indicated to the user by the position of a button, indicator lamp, or audible alarm. When the visual indicator signals that the interrupting contacts are in an open condition, or there is loss of power on the downstream receptacles, the installer is thereby prompted to correct the mis-wired condition. This approach also has its drawbacks. If the branch circuit does not include downstream receptacles, in which case the feed-thru terminals are not used, the installer is not alerted to the mis-wire condition by denial of power to either the downstream branch circuit or to the receptacle contacts. Lack of protection of the receptacle contacts is only evident to the installer if the signal or absence of signal from the visual indicator is understood. Visual indication is much more easily ignored than power denial and the mis-wire condition may not be corrected.
Historical problems with these devices include the possibility of the line and load being mis-wired by an installer. A variety of methods have been used to prevent, or attempt to prevent, mis-wiring, with varying levels of success. Labels and installation instruction sheets have been used to prevent mis-wiring, but can be ignored by the installer. Preventing the problems associated with a defective solenoid driving device is inherently more difficult. Solenoid bum-out has been revealed by testing the protective with a test button, but the result of the test can be ignored by the user.
What is needed is means for detecting a mis-wire condition that may be employed in conjunction with a physical barrier that prevents insertion of a plug into the receptacle until such time as power has been properly connected to the line terminals of the protection device